TBH, I'd go with what puddle said. Get a cheaper but still decent netbook, and spend whatever you have leftover on building a nice desktop. Netbooks are surprisingly usable if all you do on it browse and type, we've got a acer aspire one (dell mini 10s were sold out and needed something for my sister's xmas present) and I put windows 7 ultimate on it. Runs aero fine, movies, youtube, plants vs zombies (I can see slowdown on those later levels though, when zombies and peas fill up the screen) pretty much everything you'd expect from it. I wouldn't be able to stand only having that, my desktop is so much nicer
Plus having a hardware limited (per say) computer in class would help with abating distractions.